When the knee joint is affected by osteoarthritis, rheumatoid arthritis, or bone tumors or suffers a trauma, etc., the parts of the joint which are damaged, including the end portions of the femur and tibia, are resected, and an artificial knee joint replacement is mounted. As conventionally seen, an artificial knee joint consists of a combination of two femoral side members, corresponding to the medial and lateral condyles, and tibial side members, corresponding to the joint surfaces which receive the two femoral side members in such a way that they can rotate; and, artificial knee joints constructed with these femoral side members and tibial side members should perform the same movements as the body's original knee joint.
The femur and tibia are connected by many ligaments, and their extension and flexion are caused by ligaments that contracts and relaxes. In contraction, particularly, it is desirable for the same tensile force to be produced for extension and flexion, and the joint must work smoothly, without causing any pain in flexing. Especially for Japanese people who frequently sit on the floor with their legs folded underneath in Japanese style, it is necessary that more than 90° of flexion be possible. In view of the above, in the bone resection instrument proposed in Patent Reference 1, referred to below, it is confirmed that there is the same tensile force in both the extended and flexed positions, and then the bone resection range is determined.
However, the invention of this prior art confirms (measures) the tensile forces of the ligaments in the extended and flexed positions. Accordingly, the surgical operations are troublesome and require a long time. Moreover, the structure is complicated and has many movable parts and adjustment parts, and thus many operations which are laborious and require skill are needed. Furthermore, this instrument is heavy an d expensive.
Therefore, the inventors of the present application have proposed Patent Reference 2 referred to below. This is an instrument that is used when the distal end of femur is resected, and it is, fundamentally, a bone resection instrument which has a very simple structure, consisting of three parts, and it is simple to operate. It is characterized by the fact that the resection can be performed accurately along a pre-set line. However, even though resection is performed accurately along the pre-set line, problems would arise when actual artificial knee joint is mounted. Moreover, it is difficult to obtain an accurate understanding of the behavior of the joint when the joint is flexed from the extended position to the flexed position.